Method of making spark plugs



Jan. 26, A B SCHUPP 118439045 uETHoD oF MAKING sPAnx PLUGS Eiled Aug. 5. 1927 INVENTOR MIRE@ 5. .5cm/PP.

' BY MM* ATTORNEYS lll Patented Jan. 26, 1932 UNITED STATES PATENT OFFICE ALFRED B. SCI-IUP?, F RICHMOND HILL, NEW YORK, ASSIGNOR, BY MESNE ASSIGN- MENTS,

TO MOTO METER GAUGE 82; EQUIPMENT CORPORATION, OF LONG ISLAND CITY, NEW' YORK, A CORPORATION OF DELAWARE METHOD 0F MAKING SPARK PLUGS Application filed August 5, 1927.

This invention relates to the manufacture of spark plugs, and has for its object the provision of improved methods for forming an expansion space between the lower portion ot the center electrode and the adjacent inner wall ot the insulator.

The following is a description of methods for carrying out the invention in the manner at present preferred; but it will be understood that various modifications and changes may be made without departing lrom the spirit of the invention and without exceeding the scope of the claims.

The lower portion of the center electrode of a spark rplug of course expands under the high temperature of the tiring chamber of an engine; and in order to prevent such eX- pansion breaking the insulator, a small annular space is provided between said lower portion of the electrode and the wall which defines the bore of the insulator.

It is customary to attach centerl electrodes within the bore of spark plug insulators by means of cement, in order to form a sealing joint therebetween. in carrying out 'the process, it has been the practice to fill the bore of the insulator with cement in a plastic state and then pass the center electrode therethrough until its lower end projects. The assembly is then baked until the cement has hardened. Under these conditions, the electrode is, of course, cemented to the insulatorl throughout the length of the bore. Because of the absence of expansion space for the lower end of the electrode, the insulator trequently breaks in use. The present invention overcomes this objectionable feature of such cemented assemblies, and provides simple, inexpensive and etlicient methods ot forming an annular expansion space.

The invention will best be understood by reference to the accompanying drawings, wherein there is illustrated one method of carrying out the same, and in which Fig. l shows, partly in sect-ion and partly in elevation, a spark plug embodying the invention; and Fig. 2 shows, in elevation, the center electrode and terminal post assembly portion 'of such spark plug, with a coating of paraitin or other similar material applied over a part Serial No. 210,858.

ot the lower portion of the center electrode.

Like reference characters indicate like parts throughout the drawings.

Referring to the drawings, Fig. l shows a spark plug provided with a shell having a ground electrode, a coupling nut and gaskets, which orm no part of the present invention. An insulator 1, which may be of tired porcelain, is provided with a longitudinal bore, in which a center electrode 2 is adapted to be operatively seated. The upper end of the center electrode comprises a terminal post 3, provided with a recessed liange 4.

In carrying out the invention, the bore of the insulator is illed with cement in a plastic state, in accordance with the usual'practice. The lower portion 5 ot' the center electrode 2 is coated with paraffin or other suitable substance, by melting such substance and dipping the electrode therein, or in any other well-known manner. The parained end of the center electrode is then inserted in the upper end of bore and passed therethrough. The inserted cement is hardened and the paraffin is melted and allowed to run oil, leaving a small annular space between the lower portion ot sa'd electrode and the adjacent inner wall of the insulator. The paraiiin coating preferably extends from the tip of the electrode to a point opposite the lower shoulder ot the insulator, as indicated in Fig. l.

l claim:

l. The method ot .torming an expansion space between a center electrode and a spark plug insulator having a central bore, which comprises placing cement in a plastic state in said bore, applying to the lower portion of said electrode a coating of low melting point material, passing the end of said electrode through the plastic cement contained in the bore ot the insulator, hardening the cement, and removing the coating of low melting point material.

2. The method of forming a spark plug kinsulator' and electrode assembly in which the insulator has a central bore therein, which comprises placing cement in a plastic state in the bore, coating the lower portion of an electrode to increase its diameter, passing the end of said electrode through the plastic ma- (Sin ALFRED B. SCHUPP. 

